Method and apparatus for routing emergency services calls in an intelligent network

ABSTRACT

Emergency services calls may be alternate-routed in an intelligent network having at least one Service Control Point (SP) with access to a routing table, a plurality of Service Switching Points (SSP) equipped with point-in-call triggers and one or more emergency services stations (PSAP) The routing table lists a routing number for each of the emergency services stations. The method comprising the steps of:  
     (i) at a Service Switching Point, presetting a point—in-call trigger to operate at a predetermined point in a call for emergency services,  
     (ii) subsequently, during processing of an emergency services call, interrupting processing of the call and transmitting to the SCP a query signalling message requesting routing information,  
     (iii) at the SCP, accessing the routing table in dependence upon parameters in the query signalling message and obtaining a routing number for a selected emergency services operator station, forming a response signalling message including the routing number and returning such response signalling message to the SSP,  
     (iv) at the SSP, detecting the routing number, and routing the call to the emergency services operator station. There is also provided a method of translating signalling message parameters from a mobile protocol to an intelligent network protocol, and vice versa, to enable emergency services calls from mobile users to be routed to one or more PSAPs in the network.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The invention relates to a method and apparatus for handling ofcalls for emergency services in telecommunications networks and, inparticular, so-called intelligent networks.

[0003] The invention is also applicable to routing within an intelligentnetwork of emergency services calls from mobile stations.

[0004] 2. Background Art

[0005] In existing telecommunications networks, particularly in NorthAmerica, telephone calls for emergency services are routed to a PublicService Access Point (PSAP) which is staffed by emergency servicesoperators and, for reasons of reliability and continuity of service, isaccessed by way of a tandem switch dedicated to such emergency services.To access emergency services, the caller dials the emergency servicesaccess code, which in North America is 9-1-1. When the end officedetects the digits 9-1-1, instead of routing the call like a normalvoice call, it routes the call immediately to the 9-1-1 tandem switchwhich routes the call to the Public Service Access Point. In order todetermine the most appropriate emergency services centre to provide therequired services, the emergency services operator will determine thelocation of the caller by first obtaining the calling line identifier,either automatically if the tandem switch is provisioned with AutomaticNumber Identification (ANI), or by questioning the caller, and using itto access an Automatic Location Identification database and obtain thegeographical location of the caller.

[0006] Although it is usual to provide a second ALI database as a “hotspare” to ensure reliability of service, this existing way of handlingemergency services calls is not entirely satisfactory because, if thetrunks between the end office and the dedicated tandem switch, orbetween the tandem switch and the PSAP, were blocked, that PSAP couldnot supply the necessary emergency service to that caller. A furtherdisadvantage is that automatic location identification is not availablefor mobile users.

[0007] An object of the present invention is to overcome or at leastmitigate these deficiencies of existing emergency services systems. Tothis end, the present invention provides for calls for emergencyservices to be routed using out-of-band or common channel signalling.

SUMMARY OF THE INVENTION

[0008] According to one aspect of the present invention, there isprovided a method of handling emergency services calls in an intelligentnetwork having at least one Service Point (SP) equipped with softwarefor providing service features and having access to databases includinga routing table, a plurality of Service Switching Points (SSP) equippedwith call processing software having point-in-call triggers forinterrupting processing of a call and exchanging signalling messageswith the Service Point to obtain instructions for further processing ofthe call, and one or more emergency services operator stations (PSAP),the Service Switching Points and Service Point being interconnected byan out-of-band signalling system, the Service Switching Points beinginterconnected by trunks for calls therebetween, and the one or moreemergency services operator stations being each connected by trunks orlines to a respective one of said Service Switching Points, the saidrouting table listing a routing number identifying a network locationfor each of said one or more emergency services operator stations, themethod comprising the steps of:

[0009] (i) at a particular Service Switching Point, presetting apoint-in-call trigger to operate at a predetermined point in a call foremergency services,

[0010] (ii) subsequently, when said particular Service Switching Pointis processing an emergency services call, interrupting processing of thecall and transmitting to the Service Point a query signalling messagerequesting routing information,

[0011] (iii) at the Service Point, upon receipt of the query signallingmessage, accessing said routing table in dependence upon parameters inthe query signalling message and obtaining a routing numbercorresponding to a selected emergency services operator station, forminga response signalling message including the routing number and returningsuch response signalling message to said particular Service SwitchingPoint,

[0012] (iv) at said particular Service Switching Point, upon receipt ofsaid response signalling message, detecting the routing number, androuting the call to the emergency services operator station.

[0013] The method may include the prior steps, at the Service SwitchingPoint, of attempting to complete the emergency services call on thebasis of the dialled digits received from the calling party, anddetecting that the call did not complete, the point-in-call triggerbeing selected to operate following failure of such initial callcompletion attempt.

[0014] Alternatively, the point-in-call trigger may be set to interruptprocessing of all calls upon receipt of the dialled digits from thecalling party.

[0015] According to a second aspect of the present invention, there isprovided apparatus for handling emergency services calls in atelecommunications network, the apparatus comprising at least oneService Point equipped with software for providing service features anddatabases including a routing table, a plurality of Service SwitchingPoints equipped with call processing software having point-in-calltriggers for interrupting processing of a call and exchanging signallingmessages with the Service Point to obtain instructions for furtherprocessing of the call, and at least one emergency services operatorstation, the Service Switching Points and Service Point beinginterconnected by an SS7 signalling system, the Service Switching Pointsbeing interconnected by trunks for calls therebetween, and the emergencyservices station being connected by trunks to one of the ServiceSwitching Points, the routing table listing a routing number for each ofthe emergency services stations, each Service Switching Pointcomprising:

[0016] means for presetting a point-in-call trigger to operate at apredetermined point in a call for emergency services, and

[0017] means operative during processing of a call for emergencyservices to interrupt processing of the call and transmit to the ServicePoint a query signalling message requesting routing information, eachService Point comprising:

[0018] means operative, upon receipt of the query signalling message,for accessing the routing table in dependence upon parameters in thequery signalling message and obtaining a routing number for a selectedemergency services station, forming a response signalling messageincluding the routing number and returning such response signallingmessage to the requesting Service Switching Point, each ServiceSwitching Point further comprising means operative, upon receipt of saidresponse signalling message, for routing the call to the network addressfor completion to the emergency services station.

[0019] The Service Switching Point may comprise means operative toattempt to complete the emergency services call on the basis of thedialled digits, and the point-in-call trigger is set to interrupt callprocessing upon failure of such attempt.

[0020] Alternatively, each Service Switching Point may have a triggerset to interrupt all calls upon receipt of the dialled digits from theoriginating station and, in dependence thereupon, generate saidsignalling message requesting routing instructions.

[0021] According to a third aspect of the invention, there is provided atelecommunications network comprising an intelligent network portioncomprising a Service Point (SP), a plurality of Service Switching Points(SSP), one or more Public Service Access Points (PSAP) and a SignalMediation point (SMP), and a mobile network portion comprising a MobileServices Switching Centre (MSC) for routing calls from a mobile users incell sites associated with such MSC and a Home Location Register (HLR),the MSC and SSPs being interconnected by trunks for routing callstherebetween, the MSC and SSPs being connected to the SMP by SignallingSystem No. 7 (SS7) signalling links, the SMP being connected to the SCPand the HLR by respective SS7 links, the SP having access to a routingtable including entries correlating routing numbers of PSAPs with cellsite identifiers, the SMP having basic SP SS7 applications part softwarefor handling mobile or wireline TCAP messages and additional conversionsoftware and tables for translating TCAP message parameters according tomobile protocols to TCAP message parameters using intelligent networkprotocols, and vice versa,

[0022] the method comprising the steps of:

[0023] at the MSC:

[0024] upon receipt of a 9-1-1 call from a mobile station, forming aTCAP query message addressed to the destination point code of the HLRand routing the message to the SMP, the message including a mobileidentification number (MIN) for the mobile station, a cell site number,and a mobile network address for the MSC, and the dialled digits,

[0025] at the SMP:

[0026] detecting the dialled digits identifying the call as an emergencyservices call;

[0027] translating the parameters in the message as received intocorresponding AIN/IN parameters according to the intelligent networkprotocol being used by the SP,

[0028] forming an AIN/IN TCAP message including the translatedparameters, the network address of the MSC and the cell site numberbeing combined in an original Calling Party number,

[0029] overriding the destination point code of the HLR and routing themessage instead to the SP,

[0030] at the SP,

[0031] accessing the mobile routing table using the original CallingParty number from the received query and obtaining a routing number fora PSAP,

[0032] including the PSAP network address in a TCAP response message andsending this response message to the SMP, at the SMP,

[0033] translating the intelligent network parameters of the TCAPresponse message into corresponding mobile network parameters,

[0034] and routing the response message to the MSC,

[0035] at the MSC,

[0036] extracting the PSAP network address from the TCAP message androuting the emergency services call thereto via one or more of the SSPS.

[0037] According to a fourth aspect of the invention, there is providedSignal Mediation Point apparatus comprising SCP software for processingand routing TCAP messages and conversion software for translatingparameters of such TCAP messages formulated according to one or moremobile protocols into parameters according to one or more intelligentnetwork protocols, and vice versa, the SMP having signalling links forconnection to a Mobile Switching Centre, a Service Control Point and aHome Location Register, the conversion software being operative, uponreceipt of a query from the MSC containing a destination point code forthe HLR and dialled digits of an emergency services call to detect saiddigits, translate the parameters into corresponding intelligent networkparameters, change the destination point code to that of the SCP, androute the message to the SCP, and on receipt of a response from the SCP,to detect the emergency services dialled digits again, translate theparameters into corresponding mobile network parameters, and route theresponse message to the MSC.

[0038] The conversion software may determine a network address of themobile switching centre and a cell site identifier and combine both intoan original Calling Party number in the intelligent network TCAP messagesent to the SCP.

[0039] Various objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription, taken in conjunction with the accompanying drawings, ofpreferred embodiments of the invention, which are described by way ofexample only.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0040]FIG. 1, labelled PRIOR ART, is a simplified schematic diagramillustrating equipment in existing telephone systems for handling“9-1-1” calls to emergency services operators;

[0041]FIG. 2 is a simplified schematic diagram illustrating a portion ofa so-called “intelligent network” embodying a first embodiment of theinvention;

[0042]FIG. 3 is a simplified schematic diagram of a modification of thefirst embodiment of the invention;

[0043]FIG. 4 illustrates a second embodiment of the invention forhandling emergency services calls from mobile users;

[0044]FIG. 5 illustrates software modules within a signal mediationpoint of the network of FIG. 4; and

[0045]FIG. 6 illustrates message flows within the signal mediationpoint.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0046] Referring to FIG. 1, labelled PRIOR ART, existing telephonesystems, particularly in North America, comprise a Public Service AccessPoint (PSAP) 10, which is a station staffed by emergency servicesoperators and accessed by way of a tandem switch 12 dedicated to suchemergency services. In order to enable automatic identification of thelocation of the caller requesting emergency services, the PSAP 10 hasaccess, by way of a data link 14, to an automatic locationidentification (ALI) database 16. A second ALI 16′ connected by way of aseparate data link 14′ is provided as a “hot spare” to ensurereliability of service. To access emergency services, a caller usingstation apparatus 18 connected to an end office 20 dials the emergencyservices three-digit access code, which, in North America, is 9-1-1. Theend office 20 detects the digits 9-1-1 and routes the call immediatelyto the 9-1-1 tandem switch 12, which routes the call to the PSAP 10. Ifthe tandem switch 12 is provisioned with Automatic Number Identification(ANI), the calling line identifier will be available to the operatorautomatically. If it is not, the operator will question the caller toobtain the necessary information. The operator will use the calling lineidentifier to access the Automatic Location Identification database 16,in order to obtain the geographical location of the caller, determinethe most appropriate (usually the closest) emergency services centre torespond to the call, and relay the information to that centre usingknown “special” call transfer procedures and the usual data networkinterconnecting PSAPs and emergency services centres.

[0047] If the data link 14 to the Automatic Location Identificationdatabase 16 were to fail, the second ALI database 16′ could be used toensure reliability of service. If both of the ALI databases wereinaccessible, the operator could still ask the caller for his or hergeographical location. However, if the trunks 22 between the end office20 and the dedicated tandem switch 12, or the trunks 24 between thetandem switch 12 and the PSAP 10, were blocked, the PSAP 10 could notsupply the necessary emergency service to that caller.

[0048] If a normal voice call could not be completed, some form ofalternate routing via another office might be used. For emergencyservices calls, however, alternate routing via other offices, especiallyusing SS7 signalling, has not, hitherto, been used for reliabilityreasons. The originating office may attempt different trunks but, onceits list is exhausted, has no alternative but to reject the emergencyservices call. The present invention proposes providing alternaterouting of emergency services calls within intelligent networksemploying out-of-band signalling in such a way that reliabilityrequirements are met.

[0049] The out-of-band network signalling system adopted by theInternational Consultative Committee for Telephone and Telegraph(CCITT), is known as Signalling System No. 7 (SS7). For an overview ofSS7, the reader is directed to an article entitled “Signalling SystemNo. 7: A Tutorial” by A. R. Modarressi and R. A. Skorg, IEEECommunications Magazine, July 1990, which is incorporated herein byreference. The kind of SS7 system used in North America is known asCommon Channel Signalling System No. 7 (CCS7).

[0050] Telecommunications systems known as “Intelligent Networks” (IN)or “Advanced Intelligent Networks” (AIN) employ Signalling System No. 7(SS7) to exchange messages between network elements to deploy selectedservices, and between network node switching elements to set up androute calls. The messages are handled by the SS7 data communicationssystem which is separate from the trunks which carry the callsthemselves. (For a general description of intelligent network componentsand operation, the reader is directed to U.S. Pat. Nos. 5,581,610 and5,438,568 which are incorporated herein by reference.)

[0051] The main elements of such intelligent networks include ServiceSwitching Points (SSPs), Signal Transfer Points (STPs) and ServiceControl Points (SCPs) connected to each other by SS7 data links forcarrying signalling. All of these components have similar MessageTransfer Part (MTP) and Signalling Connection Control Part (SCCP)communications software to enable them to communicate with each othervia the SS7 data communications network. A Service Control Point is an“intelligence centre” with specific logic and access to applicationdatabases enabling it to deliver various combinations of features, suchas 1-800 number service and call redirection. A Signal Transfer Point(STP) is a signalling hub or concentrator, typically connecting severalService Switching Points to an SCP. A Service Switching Point (SSP) is anetwork node normally associated with a stored program central officeswitch equipped with Signalling System Number 7 (SS7) messaging links topermit communication with the SCPs and which, in addition to the usualcall processing software, has special Service Signalling Function (SSF)software. The SCP has comparable Service Control Function (SCF)software.

[0052] The Service Signalling Functions include (i) TransactionCapabilities Application Part (TCAP) messaging, which SSPs and SCPs useto determine how to process a particular call, and (ii) IntegratedServices User Part and Capability (ISDNUP) messaging which the SSPswitches use to set up a path for a particular call once it has beendetermined whence the call should be routed.

[0053] The SSP's AIN software includes a plurality of “Point-in-Calltriggers” which can be provisioned or set to interrupt call processingmomentarily and initiate a TCAP query to the SCP for instructions on howto complete the call processing. Based upon the instructions received ina TCAP message in reply, the originating end office switch seizes atrunk to a neighbouring switch and creates an Initial Address Messagewhich it sends to the neighbouring switch via the SS7 network. TheInitial Address Message includes various parameters which will controlrouting of the call to its destination.

[0054] The SSP is a logical entity. For convenience, the SSPs will bedescribed herein as performing various functions which, in reality, willbe performed by the associated physical switch.

[0055] An embodiment of the present invention in which SS7 is used toprovide emergency services will now be described with reference to FIG.2, which illustrates a portion of an “intelligent network”telecommunications system. In FIG. 2, a first subscriber apparatus 30 isconnected by subscriber loop 32 to a Service Switching Point 34 whichcomprises an end office switch. A first Public Service Access Point 36is connected to SSP 34 by trunks 38 for voice calls. A second ServiceSwitching Point 40, which comprises a second end office switch, has asecond subscriber apparatus 42 connected to it by subscriber loop 46.For purposes of this description, the subscriber apparatuses 30 and 42will be assumed to have Calling Party numbers NPA-NX1-XXXX andNPA-NX2-XXXX, respectively. A second Public Service Access Point 44 isconnected to SSP 40 by trunks 47. The two Service Switching Points 34and 40 are interconnected by trunks 48. The two Public Service Accesspoints 36 and 44 share a common Automatic Location Identificationdatabase (ALI) 50. A third Public Service Access Point 52 with which isassociated a second Automatic Location Identification database 54 isconnected by trunks 56 to a third Service Switching Point 58 which isconnected to first Service Switching Point 34 by trunks 60.

[0056] The three Service Switching points 34, 40 and 58 are connected toa Signal Transfer Point 62 by SS7 messaging links 64, 66 and 68,respectively, and the Service Transfer Point 62 is connected to aService Control Point 70 by SS7 messaging link 72.

[0057] The Service Control Point 70 has the usual SCF software anddatabases enabling it to function according to Advanced IntelligentNetwork (AIN) requirements. The SMS is not shown in FIG. 2 since itsfunctions do not affect this embodiment of the invention. For details ofthe requirements of network elements of AIN networks, the reader isdirected to the various accepted or proposed AIN standards, especially,TR-NWT-001284 AIN 0.1 SSP Generic requirements; TR-NWT-001285 AIN 0.1SCP interface; GR-1298-CORE AIN 0.2 Generic requirements; andGR-1299-CORE AIN 0.2 SCP interface.

[0058] SCP 70 is dedicated to 9-1-1, for reliability reasons, butsupports wire-line and wireless calls as will be described later. It hasspecial 9-1-1 feature software and its database will have networked9-1-1 entries in its routing table 74, which is shown separately fromthe SCP 70. This special 9-1-1 software will enable the SCP 70 toprocess 9-1-1 signalling messages only and access the 9-1-1 routingtables. Otherwise, it will be like known SCP software.

[0059] The system of FIG. 2 could route 9-1-1 calls using a variety ofPoint-In-Call triggers. Examples of 9-1-1 call routing will now bedescribed with reference to FIG. 2 and sample entries for routing table74.

[0060] Where the SSP 34 and the associated PSAP 36 are interconnected bytrunks, as in FIG. 2, it is appropriate to use the Automatic FlexibleRouting (AFR) trigger. It should be noted that, for convenience ofillustration, the PSAPs 36, 44 and 52 are shown connected directly tothe respective SSPs 34, 40 and 58. In practice, regulations may requireeach PSAP 36/44 to be connected to a tandem office, at least until ithas been accepted that embodiments of the present invention render suchdedicated tandem switches unnecessary. Hence, each of the ServiceSwitching Points 34 and 40 can be taken as representing the end office20 and tandem switch 12 of FIG. 1.

[0061] Assuming that the “Automatic Flexible Routing” trigger at SSP 34has been provisioned, when a caller using subscriber apparatus 30 dials9-1-1, the end office switch at SSP 34 will first translate the dialleddigits in the usual manner and attempt to route the call to PSAP 36, viaone of the trunks 38. If all trunks 38 are busy, which could happen ifthere were a catastrophic event, or the trunks 38 are not available totake the call for other reasons, as indicated in FIG. 2, the call willnot complete. Consequently, when the switch's route list has beenexhausted, and after checking for any code gapping requirements, theAutomatic Flexible Routing trigger at the switch of SSP 34 will causethe call-processing software to interrupt call processing and send aNetwork_Busy TCAP query to the SCP 70, via SS7 link 64, Signal TransferPoint 62 and link 72, to request alternate routing instructions. Amongother things, the TCAP query will contain the Calling Party number, i.e.NPA-NX1-XXXX, and the Called Party number, i.e. 9-1-1.

[0062] The SCP 70 will respond with an Analyze_Route response message.

[0063] The SCP 70 will detect the Calling Party number in the receivedTCAP message, access its 9-1-1 Routing Table (see Table I) to determinethat primary PSAP was PSAP 36, and select the routing number of analternative PSAP. TABLE I Wireline N-9-1-1 Routing Table 74 CallingParty # Primary PSAP Alternative PSAP NPA-NX1 PSAP 36 PSAP 44; PSAP 52NPA-NX2 PSAP 44 PSAP 34; PSAP 52

[0064] As shown in Table I, both PSAP 44 and PSAP 52 are available. TheSCP 70 will select one of them, say PSAP 44, and return to SSP 34 anAnalyze_Route TCAP message with the network address, in this example therouting number NPA-NX2-BBBB of PSAP 44 in the Called Party field.optionally, it might also include a route index. Upon receipt of thisRouting Number, the switch at SSP 34 will resume call processing and useISDNUP messaging to route the call to PSAP 44 by way of trunks 48, andSSP 40 will complete the call via trunks 47 based upon the 9-1-1 digitsin the Original Called Party field of the ISUP messages. PSAP 44 willaccess Automatic Location Identification database ALI 50 to determinecustomer information, such as specific medical condition of the caller,i.e. owner of station apparatus 30.

[0065] It should be appreciated that this system is quite flexible andcould accommodate various other trunks being unavailable. For example,if trunks 47 between PSAP 44 and SSP 40 were down also, i.e. both PSAP36 and PSAP 44 were inaccessible, the SCP 70 would route the call toPSAP 52 via SSP 58. Thus, if the SCP 70 had received a Network Busyquery because PSAP 44 were unavailable, within a recent time period, itwould mark its routing table accordingly.

[0066] If, for some reason, the SCP 70 was unaware that the trunks 47 toPSAP 44 also were unavailable, and gave SSP 34 the routing number forPSAP 44 as an alternative, SSP 34 would route the call via trunks 48 toSSP 40. SSP 40 would try to complete the call via trunks 47 and itselfencounter an AFR trigger when it could not complete. Consequently, SSP40 would send a Network_Busy TCAP query to SCP 70. Upon receipt of thissecond query, the SCP 70 would access its routing table 74 for analternative route to PSAP 40. The SCP 70 would “know” that PSAP 36 wastemporarily unavailable.

[0067] Consequently, in the Analyzed_Route TCAP message it returned toSSP 40, SCP 70 would give the routing number for PSAP 52 and route thecall to PSAP 52 via SSP 58. FIG. 2 does not show a direct trunk betweenSSP 40 and SSP 58, so SSP 40 would have to route the call to SSP 52 viatrunks 48, SSP 34, trunks 60 and SSP 58. This would entail loop-back inthe trunks 48, but this could be tolerated in these circumstances. In apractical system, of course, there would probably be a direct trunk fromSSP 40 to SSP 58.

[0068] Provision may be made for limiting the alternate PSAP selectionaccording to time-of-day, or other conditions, simply by including inthe Routing Table 74 additional entries as shown, for example, in TableII. TABLE II PSAP selection by Time-of-Day Time of Day between 12:00 amand 6:00 am Calling Party # Primary PSAP Alternative PSAP NPA-NX1 PSAP36 PSAP 52; PSAP_OutOfArea NPA-NX2 PSAP 44 PSAP 52; PSAP_OutOfArea

[0069] In this case, for example, only PSAP 52 is fully staffed between12:00 midnight and 6:00 am.

[0070] Upon receipt of a 9-1-1 call query, the Service Control Point 70would check the time of day and, if it were between midnight and 6.00am, route the 9-1-1 call to PSAP 52. To determine the caller'sparticulars, PSAP 52 would access its own ALI database 54 which willinclude similar information to that in ALI database 50. In this case,there are no other active PSAP's in the area served. Consequently, inthe event that PSAP 52 could not handle the call, for example becauseall of trunks 56 were busy, or ALI 54 inaccessible, the SCP 70 wouldroute the 9-1-1 call to a PSAP in another area, i.e. the SCP 70 wouldobtain from the routing table 74 a routing number for the OutOfArea PSAPand return it to the originating SSP 34. In the event that the OutofAreaPSAP did not have access to an ALI database with information for thecaller, the operator could seek the necessary information from thecaller.

[0071] It will be appreciated that routing to a PSAP in a different areacould be an option in the unlikely event that a major catastropherendered all three PSAP's unavailable simultaneously.

[0072] Whereas, in the embodiment of FIG. 2, each SSP has a directconnection to a PSAP and only uses the SS7 system when it fails tocomplete the 9-1-1 call directly, it is envisaged that, eventually, themajority of SSP's will access a PSAP via the network. There will notnecessarily be a dedicated tandem switch for 9-1-1 calls. It is alsoenvisaged that, as Local Number Portability and other such services areintroduced, it will be preferable for every call to be routed only aftera query to the SCP for a routing number. In such a situation, instead ofusing the Automatic Flexible Routing trigger after a normal completionattempt, a “three-digit” trigger responsive to dialled digits could beused to initiate a TCAP query on every call, including 9-1-1 calls. InNorth America, such a trigger is already used for other three digitnumbers, such as 4-1-1 to select directory enquiries.

[0073] An example of such triggering on every call will be describedwith reference to FIG. 3 which shows a portion of the network similar tothat of FIG. 2 but modified so that there is only one Public ServiceAccess Point 44, with an associated Automatic Location Identificationdatabase 50, connected as before to SSP 40. In addition to the SSPs 34,40 and 58, there is a fourth SSP 76 connected by trunks 78 and 80 toSSPs 58 and 40, respectively, and by SS7 link 82 to STP 62. In addition,an emergency services location 84 (for Fire and Medical services) isshown connected to SSP 40 by trunks 86, for voice calls, and to PSAP 44by a data link 89 of the usual data network which interconnects PSAPs,ALIs and emergency services locations. The emergency services location84 could also be connected by trunks 88 (shown in broken lines) to SSP76, in which case the SSP 40 could route calls to it via SSP 76.

[0074] The call processing software at each of the SSPs 34, 40, 58 and76 has a three-digit trigger set to trigger on receipt of the dialleddigits 9-1-1. Hence, when a calling party at station 30 at SSP 34 dials9-1-1, SSP 34 will immediately query the SCP 70 by sending it anInfo_Analyzed TCAP query containing the dialled digits as the CalledParty number and NPA-NX1-XXXX as the Calling Party number. The SCP 70will access its 9-1-1 routing database, which will be similar to thatshown in Tables I and II and determine the Routing Number of PSAP 44 andreturn it to SSP 34 in an Analyze_Route TCAP response. On receipt of theresponse, SSP 34 will route the call via SSP 40 to PSAP 44. As before,when PSAP 44 receives the call, it will automatically access its ALIdatabase 50 to determine the customer's particulars, preferably usingAutomatic Number Identification, as before. once the location has beenidentified, the PSAP operator will route the call to the emergencyservices location 84. Of course, if PSAP 44 is not available, SCP 70 mayprovide routing to an alternative, which may be out of area, as before.

[0075] It should be appreciated that both AFR Point-in-Call triggers andthree-digit 9-1-1 Point-in-Call triggers could be used together. Forexample, the originating SSP end office could trigger on the 9-1-1digits and route the call to the appropriate PSAP. In the event that, atsome point, the trunks were not available, an AFR trigger could initiatea TCAP query for an alternative route to complete the call to thedesignated PSAP or, if that were not possible, to complete the call toan alternative PSAP as described with reference to FIG. 2.

[0076] It is also envisaged that an 0_Disconnect trigger could beprovisioned (as defined in AIN 0.2) so as to initiate a query for analternate route, or an alternate PSAP, if an active emergency servicescall were interrupted, for example, by a loss of connection.

[0077] It should also be appreciated that, if SSP 40 were an end officewith a dedicated 9-1-1 tandem switch, as in FIG. 1, the SSP 34 andoffice could use an AFR trigger to obtain an alternative PSAP if thetrunks between the end office and tandem switch of SSP 40 were “down”.

[0078] It should be appreciated that the above-described embodiments ofthe invention are not limited to the use of the AFR triggers forinitiating queries to the SCP 70. It would be possible to use insteadthe Termination Attempt Trigger (TAT) which is line specific.

[0079] It is envisaged that, eventually, the SSPs might use “threedigit” Point-In-Call triggering on the dialled digits 9-1-1 withoutfirst attempting to complete the call normally. At present, however, itis not thought to be feasible to trigger on every 9-1-1 call, i.e.without first attempting to complete the call, but rather to attemptcompletion and issue a query only when the initial attempt fails.

[0080] In any of the above-described embodiments, station apparatusdedicated for use in emergencies could be accommodated. For suchapparatus, an originating Call Point-in-Call trigger could be used sothat, as soon as the dedicated station apparatus went “off hook”, theassociated SSP would generate a TCAP query for routing instructions.

[0081] An advantage of the present invention is that it can also provideautomatic location identification for 9-1-1 calls from mobile stations,i.e. cellular telephone users.

[0082] At present, call routing in the conventional mobile system isdistinct from that in the conventional wire-line system. The existingNorth American mobile telecommunications network already has SS7communication capability using IS41 messages, which are somewhat similarto TCAP messages in AIN networks. Elsewhere, Global System for MobileCommunications (GSM) messages are used instead. As illustrated in brokenlines in FIG. 1, in a conventional North American network, calls to andfrom a mobile user 90 are relayed via transceivers in intervening cellsites to a base transceiver station (BTS) 96 connected to a mobileservices switching centre (MSC) 98 by way of a base station controller(BSC) 100. A database 102 containing a Visitor Location register (VLR)is associated with MSC 98. The MSC will also have access to a HomeLocation Register (HLR) which, for convenience, is shown as part of thesame database 102. In practice, each MSC will have a local VLR but willaccess a remote HLR. The HLR stores permanent data on subscribers whopurchased a subscription from the operator to whom the HLR belongs. TheVLR is a temporary register for visiting users. When a mobile stationfrom another area enters the area covered by MSC 98, the MSC 98 willrequest data about the visiting mobile station from its home HLR via thesignalling system. The HLR/VLR database 102 could be located at the MSC98. Alternatively, as shown in FIG. 1, the MSC 98 could communicate witha remote HLR/VLR database 102 by way of a SS7 link 104. (It should benoted that, in conventional wireline switching systems, the routingtables are at the switches whereas, in mobile networks, the routingtables are at the HLR. Hence, the mobile switching centre MSC 98 mustgenerate a TCAP query for every call.)

[0083] In practice, there would probably be several switches, whetherSSPs or conventional switches, connected to the mobile switching centreMSC 98 by trunks. A normal call would be routed via any one of thoseaccording to what the HLR/VLR database 102 determined to be appropriatehaving accessed its routing tables. However, all 9-1-1 calls received byMSC 98 from mobile users would be sent to end office 20 for completionto the associated PSAP 10 via tandem switch 12. There would be nopossibility of the HLR/VLR database 102 providing a routing number toroute the 9-1-1 call elsewhere. Consequently, the conventional mobilenetwork is inflexible and unreliable because an outage of the trunksbetween end office 20 and PSAP 10, or between the MSC 98 and the endoffice 20, will result in there being no 9-1-1 service capability formobile users accessing the network via MSC 98. Moreover, for 9-1-1 callsfrom mobile users, automatic location identification is not available;the operator must ask the caller for the necessary information as tohis/her geographical location.

[0084] An embodiment of the present invention which provides flexible oralternate routing of 9-1-1 calls from a mobile user, and, in some cases,automatic location identification, will now be described with referenceto FIG. 4. The portion of the “intelligent network” shown in FIG. 4comprises some wireline components similar to those of FIG. 2, namelytwo Service Switching Points SSP 34 and SSP 40 interconnected by trunks48; Public Service Access Points 36 and 44 connected by trunks 32 and 47to SSP 34 and SSP 40, respectively; station apparatuses 30 and 42connected to SSP 34 and SSP 40, respectively; and a Service ControlPoint 70. An STP 62′ is shown connecting SSP 40 to the SMP 106 by way ofSS7 links 66′ and 66″.

[0085] In addition, the network portion of FIG. 4 includes some wirelesselements similar to those shown in FIG. 1, namely a mobile user 90communicating with a MSC 98 via transceivers in cell sites CS1 and CS2,a base transceiver station 96 and a base station controller 100.

[0086] A significant difference is that the STP 62 of the network ofFIG. 2 is replaced by a Signal Mediation Point (SMP) 106 which isconnected to SSP 34, SSP 40, MSC 98, SCP 70 and HLR 102 by SS7 links 64,66, 108, 110 and 112, respectively. Generally, the SMP 106 comprisessimilar software and data to those of an SCP. It differs, however, inthat it also has software and data for converting from wirelineparameters to wireless parameters, and vice versa. Hence, as will bedescribed in more detail later, the SMP 106 can function as a STP butcan also modify the message content, which a STP cannot normally do.

[0087] The Routing Table 114 accessed by the SCP 70 includes mobileinformation in addition to the entries of Routing Table 74 of FIG. 2.For example, as shown in Table III, the additional mobile informationincludes an entry for the Calling Party Number of the mobile user 90,namely NPA-NX4-XXXX; the MSCID for MSC 98; cell site identifiers forcell sites CS1 and CS2 and, for each cell site identifier, Primary andAlternate PSAP routing numbers. Conveniently, the cell site identifiersare linked to the corresponding PSAP locations on a geographical basis.TABLE III Mobile N-911 Routing Table Mobile-Calling Cell Primary PartyNumber MSCID Site PSAP Alternate PSAP NPA-NX4-XXXX NPA-NX3 XXX1 PSAP-1PSAP-2, PSAP-3 NPA-NX3 XXX2 PSAP-2 PSAP-1, PSAP-3 Time of Day From 12 amto 6 am NPA-NX4-XXXX NPA-NX3 XXX1 PSAP-1 PSAP_OutofArea NPA-NX3 XXX2PSAP-3 PSAP_OutofArea

[0088] The SMP 106 will have similar data to that in columns 1-3 ofTable II enabling it to determine the cell site identifier from the cellsite number in the incoming query from the MSC 98.

[0089] Also shown in FIG. 4 is a Service Management System (SMS) 116which provides for provisioning and updating of customer data in thedatabases at the SCP 70, the SMP 106 and the ALI 50 by way of X.25 links118, 120 and 122, respectively, enabling it to synchronize the data inthem. The SMS 116 is a known element of intelligent networks and itsnormal functions are defined in the various standards, such as AIN 0.1.In FIG. 4, the various trunks between the SSPs are not shown. Only thetrunks between MSC 98 and SSP 34, and between SSP 34 and SSP 40 areshown, together with the SS7 links.

[0090] The MSC 98 has ISDNUP capability enabling it to exchange ISDNUPmessages with the wireline service switching points SSP 34 and SSP 40 toset up the trunks for the call.

[0091] The MSC 98 communicates with the HLR 102 by way of the SMP 106,rather than direct. For a normal call, the MSC 98 will use IS41 messagesto communicate with the HLR 102 by way of the SMP 106 to obtain thenecessary routing number or route index and then will route the call viathe appropriate trunk group. Although the MSC 98 is shown with trunks toSSP 34 only, in practice it would be connected to other SSPs also. It isno longer limited to routing all 9-1-1 calls to the one SSP 34, however,but could route a 9-1-1 call to a PSAP elsewhere in the network.

[0092] When the mobile station user first switches on the cellulartelephone of mobile station 90, it will automatically transmit a messageidentifying itself. When the MSC 98 receives this message, it willincorporate the mobile station's ID into an IS41 message and send it tothe HLR 102, via the SMP 106, to effect registration. The HLR 102 willcheck the identification against its database (not shown) to ensure thatit is valid. When, subsequently, the mobile user 90 makes or receives anormal call, the MSC 98 will exchange IS41 messages with the HLR 102,via the SMP 106, to set up the call.

[0093] If a mobile user enters the area, a temporary registrationprocess will be effected using the VLR register of database 102, inknown manner.

[0094] For normal calls from mobile user 90, including initialregistration calls, the SMP 106 acts like a STP, i.e. it is virtuallytransparent and simply does whatever correlation is necessary to routethe message from the MSC 98 to the HLR 102, or vice versa. It does notchange the content of the message.

[0095] For a 9-1-1 call from mobile user 90, however, the process isdifferent. The Signalling Mediation Point 106 intercepts the query sentfrom the MSC 98 to the HLR/VLR database 102 and redirects it to the SCP70 instead. At least at present, the SCP 70 will not be able to“understand” IS41 queries, so the SMP 106 translates the query to AIN orIN format, whichever is required by SCP 70. The SCP 70 accesses itsrouting table 114, obtains the routing number of the appropriate PSAP,36 or 44, and returns a response to the MSC 98 via the SMP 70. The SMP106 translates the response from the SCP 70 from AIN/IN format to IS41format before conveying it to the MSC 98.

[0096] The various software components of the SMP 106 which are involvedin this transaction are depicted in FIG. 5 and typical call flow throughthe SMP 106 in FIG. 6. Thus, as shown, the SMP 106 contains MessageTransfer Part (MTP) and Signalling Connection Control Part (SCCP)modules and Originating Point Code/Destination Point Code (OPC/DPC)tables which allow it to function like a STP, i.e. detect information inthe Service Information Octet (SIO) and route TCAP messages accordingly.

[0097] The SMP 106 also has components normally found in a ServiceControl Point, namely a TCAP APPLICATIONS module, a component layer withfour TCAP domain modules namely IS-41 Mobile Applications Part Module(ISM MAP), a GSM MAP, and AIN and IN domains, and CUSTOMER DATA. The SMP106 also has a SMS software module for interfacing with the SMS 116 toallow updates, etc. Operation of these components is according to theestablished standards and so will not be described herein.

[0098] In addition, the SMP 106 has CONVERSION software for convertingbetween IS41/GSM protocol parameters and AIN/IN protocol parameters, aswill be described in more detail later.

[0099] It should be noted that FIG. 5 is a conceptual illustration. Inpractice, functions of the various modules will overlap. The MTP moduleof SMP 106 may handle messages from SSP switches directly, as indicatedat 120 in FIG. 5, or indirectly, in the latter case via a STP, asindicated at 122.

[0100] As illustrated by broken line path 124 in FIG. 6, “normal”Message Signal Units (MSU), including FISU, LSSU and SNM messages fromSSPs 34 and 40 or the MSC 98 simply traverse the physical layer L1 andlink layer L2 of the MTP and are redirected, in known manner, using theOrigin Point Code and Destination Point Code (OPC/DPC) tables and theSIO, back out again to their appropriate destinations.

[0101] If a TCAP message for a normal call is received, it will followthe path shown by chain link line 126 and be screened by the higherlayers. The CONVERSION software will not detect the digits 9-1-1 and sowill not do any translation.

[0102] If the message is an IS41 or GSM RouteRequest message for amobile 9-1-1 call, and hence has these digits in the dialled digitsfield, it will follow path 125 and be routed as before to the CONVERSIONSOFTWARE module, but in this case the CONVERSION software will detectthe 9-1-1 dialled digits and translate the parameters into AIN or INparameters.

[0103] The CONVERSION software will pass the converted parameters to theappropriate AIN/IN component layer module which will include them in anInfo_Analyzed message including the destination Point Code of theappropriate SCP 70. The Info_Analyzed message will be processed throughthe MTP layers and routed to the SCP 70, which will process it in theusual way. When the SCP 70 issues an Analyze_Route message in reply, theSMP 106 will process it in the reverse order to provide a correspondingIS41 RouteRequest response message.

[0104] Table IV shows the mapping between IS41 or GSM messages and AIN0.1 messages and between parameters in those messages. TABLE IV IS-41GSM AIN 0.1 Message: Route Request Provide Info_Analyzed/ Roaming NumberAnalyze_Route Parameters: MIN MSISDN Calling Party Number (of Mobile 90)Routing Number Roaming Number Destination Number (10 digits) OriginalCalling Number: NPA-NXX-XXXX MSCID IMSI NPA-NXX Cell Site # Cell Site #XXXX Dialled Digits Dialled Digits Dialled Digits

[0105] For the specific example of FIG. 4, the Original Calling Numberwill comprise the NPA-NX3 of the MSC 98 and the four digit identifierXXX2 of cell site CS2.

[0106] The IS41 parameter MIN is a mobile identification number assignedto, and permanently recorded in, the cellular telephone set 90. In NorthAmerica, it comprises a ten digit number in North American dialling planformat. However, elsewhere it could be in a different format, and evencomprise from 7 to 20 digits, depending upon the service provider. Sucha number could not be recognized by SCP 70, in which case the SMP 106'sconversion software would convert the MIN into a Calling Party number inthe form NPA-NXX-XXXX used in AIN 0.1.

[0107] If an SSP receives a call for a mobile user, such as mobile user90, the NPA-NX4 number, it will route the call automatically to MSC 98.

[0108] The MSC 98 itself will have a first network address MSCIDassigned to it within the mobile network and used for communication withthe HLR. Within the wireline network, however, it has a second networkaddress NPA-NXX assigned to it. The SMP 106 will convert from either tothe other.

[0109] The Original Calling Number must have 10 digits. It includes theNPA-NXX of the MSC 98 as its first six digits. The last four digits arethe cell site identifier XXXX.

[0110] The destination number of the selected PSAP will be included inthe AIN/IN response message from the SCP 70 and will be converted intothe IS-41 Routing Number used by the mobile switch MSC 98 as the addressto which the call is to be routed.

[0111] Thus, assuming that mobile station 90 (FIG. 4) makes a 9-1-1 calland is using IS-41, the corresponding message sent to the SMP 106 by theMSC 98, and addressed to the HLR/VLR 102, will comprise a RouteRequestquery including a “toggle” flag set to indicate that it is a queryrather than a response. (If the GSM protocol is used, the message willbe a Provide Roaming Number message with a flag to determine whether itis a query or a response.) The Route Request message will include theMIN of the mobile user 90, the digits 9-1-1 as the Dialled Digits, theMSCID for MSC 98, and the complete Cell Site number, i.e. identifyingthe sector within cell CS2 within which the 9-1-1 call originated (thelatter as determined by the base transceiver station).

[0112] On receipt of the IS41 message, the SMP 106 will detect that thedialled digits comprise the digits 9-1-1. Consequently, the conversionsoftware of SMP 106 will convert the parameters of the IS41 messageaccording to Table IV and include them in an Info Analyzed message. Itwill also supply to the SCCP the destination point code of SCP 70 whichthe SCCP/MTP layers will use to route the Info_Analyzed message to theSCP 70. The SCP 70 will access its routing table 114 using the OriginalCalling Number which comprises the address NPA-NX3 of mobile switch 98and the four digit cell site number XXX2 identifying the origin of thecall within cell site CS2 to determine the primary PSAP for thatparticular cell site, in this case PSAP 44 because it is closest. Onceagain, the SCP 70 will have alternative PSAPs available as shown inTable III and will make the determination as described previously.

[0113] The SCP 70 will then select the routing number for the selectedPSAP 44, include it as the Called Party number in a TCAP Analyze_Routemessage and send the message to the SMP 106. It will leave the CallingParty number, mobile switch NPA-NX4 and Original Calling Number fieldsunchanged. Upon receipt of this TCAP Analyze_Route message, the SMP106's TCAP APPLICATIONS layer will correlate the response with the queryusing the Transaction I.D. in known manner. The SMP 106 will convert theparameters back into IS41 format according to Table IV and include themin an IS41 message which it will return to mobile switch MSC 98. The MSC98 will use the new Routing Number to route the call to the SSP 40 whichserves as an end office for the PSAP 44. The SSP 40 will detect theRouting Number in the Called Party number field and complete the call tothe PSAP 44. Of course, the SSP 40 could be a combination of an endoffice and a tandem office, such as those already in existence anddescribed with reference to FIG. 1.

[0114] It should be noted that, in AIN, the Routing Number could eplaced in either the Destination Number or the Called Party umber fieldand the terminating SSP could complete the call.

[0115] It should be appreciated that the MSCID/cell site information inthe original calling Number could be used for Automatic LocationIdentification by the PSAP. The ALI 50 would then be provided withsoftware and data to identify a geographical location of a cell sitefrom this MSCID/cell site information. Because the SCP 70 selects theappropriate PSAP based upon the cell site number from which the calloriginated, the mobile user might no longer be at the location whereemergency services were needed. It would be the responsibility of thePSAP operator to interview the caller and determine whether or not thecaller was still at the site of the emergency when the 9-1-1 call wasplaced.

[0116] It should be appreciated that the SMP, with its capability forconverting between wireline and wireless protocols, is not limited totranslation of 9-1-1 calls but could be used for providing other AIN/INservices to mobile users.

[0117] It should be appreciated that although only conversion from IS41to AIN has been described in the specific example, a person skilled inthis art would be able to effect conversion from GSM to AIN or IN, orfrom IS41 to IN, in an analogous manner and without undueexperimentation.

[0118] Although the foregoing description of a preferred embodimentrelates to a so-called “intelligent network”, it should be appreciatedthat a skilled person would be able to implement the invention in othersystems which use out-of-band signalling.

[0119] Although embodiments of the invention have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and not to be taken by way ofthe limitation, the spirit and scope of the present invention beinglimited only by the appended claims.

1. A method of handling emergency services calls in an intelligentnetwork having at least one Service Point (SP) equipped with softwarefor providing service features and having access to databases includinga routing table, a plurality of Service Switching Points (SSP) equippedwith call processing software having point-in-call triggers forinterrupting processing of a call and exchanging TCAP signallingmessages with the Service Point to obtain instructions for furtherprocessing of the call, and one or more emergency services operatorstations (PSAP), the Service Switching Points and Service Point beinginterconnected by an SS7 signalling system, the Service Switching Pointsbeing interconnected by trunks for calls therebetween, and the one ormore emergency services operator stations being each connected by trunksor lines to a respective one of said Service Switching Points, the saidrouting table listing a routing number identifying a network locationfor each of said one or more emergency services operator stations, themethod comprising the steps of: (i) at a particular Service SwitchingPoint, presetting a point-in-call trigger to operate at a predeterminedpoint in a call for emergency services, (ii) subsequently, when saidparticular Service Switching Point is processing an emergency servicescall, interrupting processing of the call and transmitting to theService Point a query signalling message requesting routing information,(iii) at the Service Point, upon receipt of the query signallingmessage, accessing said routing table in dependence upon parameters inthe query signalling message and obtaining a routing numbercorresponding to a selected emergency services operator station, forminga response signalling message including the routing number and returningsuch response signalling message to said particular Service SwitchingPoint, (iv) at said particular Service Switching Point, upon receipt ofsaid response signalling message, detecting the routing number, androuting the call to the emergency services operator station.
 2. A methodaccording to claim 1, wherein the point-in-call trigger is selected tooperate following failure of an initial call completion attempt, and themethod includes the steps, at the Service Switching Point, of attemptingto complete the emergency services call on the basis of the dialleddigits received from the calling party, and detecting that the initialcall did not complete, said step of transmitting said query signallingmessage being contingent upon such step of detecting that the initialcall did not complete.
 3. A method according to claim 1, wherein thepoint-in-call trigger is set to interrupt all calls upon receipt ofdialled digits from the calling party identifying that the call is foran emergency services station.
 4. Apparatus for handling emergencyservices calls in a telecommunications network employing TCAPsignalling, comprising at least one Service Point equipped with softwarefor providing service features and having access to databases includinga routing table, a plurality of Service Switching Points equipped withcall processing software having point-in-call triggers for interruptingprocessing of a call and exchanging TCAP signalling messages with theService Point to obtain instructions for further processing of the call,and one or more emergency services operator stations, the ServiceSwitching Points and Service Point being interconnected by an SS7signalling system, the Service Switching Points being interconnected bytrunks for calls therebetween, and each of the emergency servicesoperator stations being connected by trunks to a respective one of saidone or more of the Service Switching Points, the routing table listing arouting number for each of said one or more emergency services operatorstations; each Service Switching Point comprising (i) means forpresetting a point-in-call trigger to operate at a predetermined triggerdetection point in the precessing of a call for emergency services, and(ii) means operative during processing of a call for emergency servicesto interrupt processing of the call in response to said trigger andtransmit to the Service Point a signalling message requesting routinginformation, each Service Point comprising (iii) means operative, uponreceipt of said signalling message, for accessing said routing table independence upon parameters in said signalling message and obtaining arouting number corresponding to a selected emergency services operatorstation, forming a response signalling message including the routingnumber and returning such response signalling message to the requestingService Switching Point, each Service Switching Point further comprising(iv) means operative, upon receipt of said response signalling message,for routing the call to the network address for completion to theemergency services station.
 5. Apparatus according to claim 4, whereineach Service Switching Point comprises means operative to attempt tocomplete the emergency services call on the basis of digits dialled bythe caller and identifying that the call is for an emergency servicesstation, and the point-in-call trigger is set to interrupt callprocessing upon failure of such attempt.
 6. Apparatus according to claim4, wherein said trigger is set to interrupt all calls upon receipt, fromthe originating station, of dialled digits identifying that the call isfor an emergency services station.
 7. In a telecommunications networkcomprising a Service Point (SP), a plurality of Service Switching Points(SSP), one or more Public Service Access Points (PSAP) and a SignalMediation point (SMP), and a mobile network portion comprising a MobileServices Switching Centre (MSC) for routing calls from mobile users incell sites associated with such MSC and Home Location Register (HLR),the MSC and SSPs being interconnected by trunks for routing callstherebetween, the SC and SSPs being connected to the SMP by SignallingSystem No. 7 (SS7) signalling links, the SMP being connected to the SCPand the HLR by respective SS7 links, the SP having access to a routingtable including entries correlating routing numbers of PSAPs with cellsite identifiers, the SMP having basic SCP software for handling mobileor wireline TCAP messages and additional conversion software and tablesfor translating TCAP message parameters according to mobile protocols toTCAP message parameters using intelligent network protocols, and viceversa, the method comprising the steps of: at the MSC: upon receipt of a9-1-1 call from a mobile station, forming a TCAP query message addressedto the destination point code of the HLR and routing the message to theSMP, the message including a mobile identification number (MIN) for themobile station, a cell site number, and a mobile network address for theMSC, and the dialled digits, at the SMP: detecting the dialled digitsidentifying the call as an emergency services call; translating theparameters in the message as received into corresponding AIN/INparameters according to the intelligent network protocol being used bythe SP, forming an AIN/IN TCAP message including the translatedparameters, the network address of the MSC and the cell site numberbeing combined in an original Calling Party number, overriding thedestination point code of the HLR and routing the message to the SP, atthe SP, accessing the mobile routing table using the original CallingParty number from the received query and obtaining a routing number fora PSAP, including the PSAP routing number in a TCAP response message andsending this response message to the SMP, at the SMP, translating theintelligent network parameters of the TCAP response message intocorresponding mobile network parameters, and routing the responsemessage to the MSC, at the MSC, extracting the PSAP routing number fromthe TCAP message and routing the emergency services call thereto via oneor more of the SSPs.
 8. Signal Mediation Point apparatus comprising SS7software for processing TCAP messages and conversion software fortranslating parameters of such TCAP messages formulated according to onemobile protocol into parameters according to a different intelligentnetwork protocol, and vice versa, the SMP having signalling links forconnection to a Mobile Switching Centre, a Service Point (SP) and a HomeLocation Register, the conversion software being operative, upon receiptof a query from the MSC containing a destination point code for the HLRand dialled digits of an emergency services call to detect said digits,translate the parameters into corresponding intelligent networkparameters, override the destination point code of the HLR and route themessage to the SP, and on receipt of a response from the SP, translatethe parameters into corresponding mobile network parameters, and routethe response message to the MSC.
 9. Apparatus according to claim 8,wherein the conversion software is operative to determine a networkaddress of the mobile switching centre and a cell site identifier andcombine both into an Original Calling Party number in the intelligentnetwork TCAP message sent to the SP.